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Spring Boot优雅地处理404异常

开发技术 开发技术 4天前 9次浏览

背景

在使用SpringBoot的过程中,你肯定遇到过404错误。比如下面的代码:

@RestController
@RequestMapping(value = "/hello")
public class HelloWorldController {
    @RequestMapping("/test")
    public Object getObject1(HttpServletRequest request){
        Response response = new Response();
        response.success("请求成功...");
        response.setResponseTime();
        return response;
    }
}

当我们使用错误的请求地址(POST http://127.0.0.1:8888/hello/test1?id=98)进行请求时,会报下面的错误:

{
  "timestamp": "2020-11-19T08:30:48.844+0000",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/hello/test1"
}

虽然上面的返回很清楚,但是我们的接口需要返回统一的格式,比如:

{
    "rtnCode":"9999",
    "rtnMsg":"404 /hello/test1 Not Found"
}

这时候你可能会想有Spring的统一异常处理,在Controller类上加@RestControllerAdvice注解。但是这种做法并不能统一处理404错误。

404错误产生的原因

产生404的原因是我们调了一个不存在的接口,但是为什么会返回下面的json报错呢?我们先从Spring的源代码分析下。

{
  "timestamp": "2020-11-19T08:30:48.844+0000",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/hello/test1"
}

为了代码简单起见,这边直接从DispatcherServlet的doDispatch方法开始分析。(如果不知道为什么要从这边开始,你还要熟悉下SpringMVC的源代码)。

... 省略部分代码....
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
... 省略部分代码

Spring MVC会根据请求URL的不同,配置的RequestMapping的不同,为请求匹配不同的HandlerAdapter。

对于上面的请求地址:http://127.0.0.1:8888/hello/test1?id=98匹配到的HandlerAdapter是HttpRequestHandlerAdapter。

我们直接进入到HttpRequestHandlerAdapter中看下这个类的handle方法。

@Override
@Nullable
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
    throws Exception {
    ((HttpRequestHandler) handler).handleRequest(request, response);
    return null;
}

这个方法没什么内容,直接是调用了HttpRequestHandler类的handleRequest(request, response)方法。所以直接进入这个方法看下吧。

@Override
public void handleRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

    // For very general mappings (e.g. "/") we need to check 404 first
    Resource resource = getResource(request);
    if (resource == null) {
        logger.trace("No matching resource found - returning 404");
        // 这个方法很简单,就是设置404响应码,然后将Response的errorState状态从0设置成1
        response.sendError(HttpServletResponse.SC_NOT_FOUND);
        // 直接返回
        return;
    }
    ... 省略部分方法
}

这个方法很简单,就是设置404响应码,将Response的errorState状态从0设置成1,然后就返回响应了。整个过程并没有发生任何异常,所以不能触发Spring的全局异常处理机制

到这边还有一个问题没有解决:就是下面的404提示信息是怎么返回的。

{
  "timestamp": "2020-11-19T08:30:48.844+0000",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/hello/test1"
}

我们继续往下看。Response响应被返回,进入org.apache.catalina.core.StandardHostValve类的invoke方法进行处理。(不要问我为什么知道是在这里?Debug的能力是需要自己摸索出来的,自己调试多了,你也就会了)

@Override
public final void invoke(Request request, Response response)
    throws IOException, ServletException {
    
    Context context = request.getContext();
    if (context == null) {
        response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
                           sm.getString("standardHost.noContext"));
        return;
    }

    if (request.isAsyncSupported()) {
        request.setAsyncSupported(context.getPipeline().isAsyncSupported());
    }

    boolean asyncAtStart = request.isAsync();
    boolean asyncDispatching = request.isAsyncDispatching();

    try {
        context.bind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER);
        if (!asyncAtStart && !context.fireRequestInitEvent(request.getRequest())) {
            return;
        }
        try {
            if (!asyncAtStart || asyncDispatching) {
                context.getPipeline().getFirst().invoke(request, response);
            } else {
                if (!response.isErrorReportRequired()) {
                    throw new IllegalStateException(sm.getString("standardHost.asyncStateError"));
                }
            }
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            container.getLogger().error("Exception Processing " + request.getRequestURI(), t);
            if (!response.isErrorReportRequired()) {
                request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, t);
                throwable(request, response, t);
            }
        }
        response.setSuspended(false);

        Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);
        if (!context.getState().isAvailable()) {
            return;
        }
        // 在这里判断请求是不是发生了错误,错误的话就进入StandardHostValve的status(Request request, Response response)方法。
        // Look for (and render if found) an application level error page
        if (response.isErrorReportRequired()) {
            if (t != null) {
                throwable(request, response, t);
            } else {
                status(request, response);
            }
        }

        if (!request.isAsync() && !asyncAtStart) {
            context.fireRequestDestroyEvent(request.getRequest());
        }
    } finally {
        // Access a session (if present) to update last accessed time, based
        // on a strict interpretation of the specification
        if (ACCESS_SESSION) {
            request.getSession(false);
        }
        context.unbind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER);
    }
  }

这个方法会根据返回的响应判断是不是发生了错了,如果发生了error,则进入StandardHostValve的status(Request request, Response response)方法。这个方法“兜兜转转”又进入了StandardHostValve的custom(Request request, Response response,ErrorPage errorPage)方法。这个方法中将请求重新forward到了”/error”接口。

 private boolean custom(Request request, Response response,
                             ErrorPage errorPage) {

        if (container.getLogger().isDebugEnabled()) {
            container.getLogger().debug("Processing " + errorPage);
        }
        try {
            // Forward control to the specified location
            ServletContext servletContext =
                request.getContext().getServletContext();
            RequestDispatcher rd =
                servletContext.getRequestDispatcher(errorPage.getLocation());
            if (rd == null) {
                container.getLogger().error(
                    sm.getString("standardHostValue.customStatusFailed", errorPage.getLocation()));
                return false;
            }
            if (response.isCommitted()) {
                rd.include(request.getRequest(), response.getResponse());
            } else {
                // Reset the response (keeping the real error code and message)
                response.resetBuffer(true);
                response.setContentLength(-1);
                // 1: 重新forward请求到/error接口
                rd.forward(request.getRequest(), response.getResponse());
                response.setSuspended(false);
            }
            return true;
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            container.getLogger().error("Exception Processing " + errorPage, t);
            return false;
        }
    }

上面标号1处的代码重新将请求forward到了/error接口。所以如果我们开着Debug日志的话,你会在后台看到下面的日志。

[http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.DispatcherServlet:891 - DispatcherServlet with name 'dispatcherServlet' processing POST request for [/error]
2020-11-19 19:04:04.280 [http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping:313 - Looking up handler method for path /error
2020-11-19 19:04:04.281 [http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping:320 - Returning handler method [public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)]
2020-11-19 19:04:04.281 [http-nio-8888-exec-7] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory:255 - Returning cached instance of singleton bean 'basicErrorController'

上面是/error的请求日志。到这边还是没说明为什么能返回json格式的404返回格式。我们继续往下看。

到这边为止,我们好像没有任何线索了。但是如果仔细看上面日志的话,你会发现这个接口的处理方法是:

org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)]

我们打开BasicErrorController这个类的源代码,一切豁然开朗。

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
    @RequestMapping(produces = "text/html")
    public ModelAndView errorHtml(HttpServletRequest request,
            HttpServletResponse response) {
        HttpStatus status = getStatus(request);
        Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
                request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
        response.setStatus(status.value());
        ModelAndView modelAndView = resolveErrorView(request, response, status, model);
        return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
    }

    @RequestMapping
    @ResponseBody
    public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
        Map<String, Object> body = getErrorAttributes(request,
                isIncludeStackTrace(request, MediaType.ALL));
        HttpStatus status = getStatus(request);
        return new ResponseEntity<Map<String, Object>>(body, status);
    }
    ... 省略部分方法
}

BasicErrorController是Spring默认配置的一个Controller,默认处理/error请求。BasicErrorController提供两种返回错误一种是页面返回、当你是页面请求的时候就会返回页面,另外一种是json请求的时候就会返回json错误。

自定义404错误处理类

我们先看下BasicErrorController是在哪里进行配置的。

在IDEA中,查看BasicErrorController的usage,我们发现这个类是在ErrorMvcAutoConfiguration中自动配置的。

@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
// Load before the main WebMvcAutoConfiguration so that the error View is available
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, ResourceProperties.class })
public class ErrorMvcAutoConfiguration {
    
    @Bean
	@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
	public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
		return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
				this.errorViewResolvers);
	}
	... 省略部分代码
}

从上面的配置中可以看出来,只要我们自己配置一个ErrorController,就可以覆盖掉BasicErrorController的行为。

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class CustomErrorController extends BasicErrorController {

    @Value("${server.error.path:${error.path:/error}}")
    private String path;

    public CustomErrorController(ServerProperties serverProperties) {
        super(new DefaultErrorAttributes(), serverProperties.getError());
    }

    /**
     * 覆盖默认的JSON响应
     */
    @Override
    public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {

        HttpStatus status = getStatus(request);
        Map<String, Object> map = new HashMap<String, Object>(16);
        Map<String, Object> originalMsgMap = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.ALL));
        String path = (String)originalMsgMap.get("path");
        String error = (String)originalMsgMap.get("error");
        String message = (String)originalMsgMap.get("message");
        StringJoiner joiner = new StringJoiner(",","[","]");
        joiner.add(path).add(error).add(message);
        map.put("rtnCode", "9999");
        map.put("rtnMsg", joiner.toString());
        return new ResponseEntity<Map<String, Object>>(map, status);
    }

    /**
     * 覆盖默认的HTML响应
     */
    @Override
    public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
        //请求的状态
        HttpStatus status = getStatus(request);
        response.setStatus(getStatus(request).value());
        Map<String, Object> model = getErrorAttributes(request,
                isIncludeStackTrace(request, MediaType.TEXT_HTML));
        ModelAndView modelAndView = resolveErrorView(request, response, status, model);
        //指定自定义的视图
        return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
    }
}

默认的错误路径是/error,我们可以通过以下配置进行覆盖:

server:
  error:
    path: /xxx

更详细的内容请参考Spring Boot的章节。

简单总结

  • 如果在过滤器(Filter)中发生异常,或者调用的接口不存在,Spring会直接将Response的errorStatus状态设置成1,将http响应码设置为500或者404,Tomcat检测到errorStatus为1时,会将请求重现forward到/error接口;
  • 如果请求已经进入了Controller的处理方法,这时发生了异常,如果没有配置Spring的全局异常机制,那么请求还是会被forward到/error接口,如果配置了全局异常处理,Controller中的异常会被捕获;
  • 继承BasicErrorController就可以覆盖原有的错误处理方式。

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